chore: dotnet upgrade from 6.0 -> 8.0

[iankhou]

Issue #32804

Closes #32804

Reason for this change

New projects in C# and F# are initialized using .NET6.0, which was designated EOL 12 NOV 2024.

Description of changes

Upgraded .NET from 6.0 (EOL) -> 8.0 (LTS) for new projects in C# and F#.

Describe any new or updated permissions being added

No permissions changes.

Description of how you validated changes

Changed unit tests to check for .NET8.0 instead of .NET6.0, and ran them successfully.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[aws-cdk-automation]

The pull request linter has failed. See the aws-cdk-automation comment below for failure reasons. If you believe this pull request should receive an exemption, please comment and provide a justification.

A comment requesting an exemption should contain the text Exemption Request. Additionally, if clarification is needed add Clarification Request to a comment.

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.40%. Comparing base (ef135ef) to head (25e7b43).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #32894   +/-   ##
=======================================
  Coverage   81.40%   81.40%           
=======================================
  Files         223      223           
  Lines       13727    13727           
  Branches     2411     2411           
=======================================
  Hits        11175    11175           
  Misses       2274     2274           
  Partials      278      278           

Flag	Coverage Δ
suite.unit	81.40% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
packages/aws-cdk	80.74% <ø> (ø)
packages/aws-cdk-lib/core	82.10% <ø> (ø)

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

➡️ PR build request submitted to test-main-pipeline ⬅️

A maintainer must now check the pipeline and add the pr-linter/cli-integ-tested label once the pipeline succeeds.

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 25e7b43
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

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